1. Field of the Invention
The present invention relates to a method and system for compressing motion image information with a high compression ration and at a high speed.
2. Description of the Related Art
In earlier image signal transmission, an image signal is first converted to another signal and then coded by assigning proper codes selected according to the statistical feature of the converted signal. When the image has high redundancy within a frame, as is the case with an image including a regular pattern or a plain image, there is a high correlation between adjacent pixels, and thus it is possible to predict, to a certain degree, a pixel value to be coded next from a pixel value which has already been coded. Therefore, if components which could not be predicted are extracted, the coding is performed only for those components which could not be predicted, thereby it becomes possible to compress information with a large compression ratio. This technique is called the predictive coding.
In the case of a motion image in a video telephone or the like, images of adjacent frames are very similar to each other, and thus the temporal change is limited. Such temporal redundancy can be removed by means of interframe predictive coding on the basis of interframe prediction. In this case, a block code is generally employed in which one codeword is assigned to one symbol, and one frame is divided into a plurality of pixel blocks so that the luminance difference within each block becomes smaller than within the entire frame. The smaller luminance difference within each block allows compression of information. This technique is called block coding.
Entropy coding is known in the art as a coding technique, which achieves data compression by assigning a high efficiency code to the converted signal. Huffman coding is known as a method for generating a high efficiency code. A representative example of the high efficiency code is an arithmetic code in which a probability numeric line is divided into segments in accordance with the occurrence probability of a symbol system, and a binary decimal number indicating a location in a segment is employed as a code for the symbol system. Codewords are generated one by one by performing the arithmetic process described above.
A three-step block coding system is known in the art as a technique for coding an image signal in an efficient manner. This technique consists of three steps: sampling; conversion; and quantification. In this technique, in order to retain a two-dimensional resolution and high-frequency components of a given image signal, it is generally required to perform sampling at a frequency twice the highest frequency component.
However, in the conventional image signal compression technique, because the complicated block coding process is employed, it is difficult to compress image data by means of predictive coding with a high compression ratio and at a high speed.
When differential information is compressed in the motion image compression process, that is, when successive values A1 and A2 are predicted to be similar to each other and when the value A1 is known before the value A2 occurs, the difference A2-A1 is regarded as having a value near 0, and compression is performed using the conventional Huffman code or arithmetic code. However, if A1 and A2 can each take one of values 0, . . . , n, the difference A2-A1 can have one of 2n+1 values. As a result, it is required to prepare 2n+1 Huffman code words. However, A2 can actually take one of n values, and thus n codes are not used from the local point of view. This circuit that the code includes a large amount of redundancy.
In view of the above problems in the conventional techniques, it is an object of the present invention to provide a method and a system for compressing motion image information by means of predictive coding with a high compression ratio and at a high speed.
According to an aspect of the present invention, there is provided a method of compressing motion image information by means of comparing spatially or temporally adjacent pixels to each other and outputting differential information thereby reducing redundant information between frames, the method including the steps of: comparing corresponding pixels to each other between frames, detecting an area where the absolute values of pixel differences are greater than a given parameter, and storing the detected area and the other area into the form of a 1-bit bit map; and compressing information in the area where the absolute values of pixel differences are greater than the parameter.
According to another aspect of the present invention, there can be provided a method of compressing motion image information by means of comparing spatially or temporally adjacent pixels to each other and outputting differential information thereby reducing redundant information between frames, the method including the steps of: comparing corresponding pixels to each other between frames, detecting an area where the absolute values of pixel differences are greater than a given parameter, and storing the detected area and the other area into the form of a 1-bit bit map; and compressing information in the area where the absolute values of pixel differences are greater than the parameter and processing (deleting) the other area, where the absolute values of pixel differences are not greater than the parameter, as an area where there is no change in pixel value between frames. In this case, the 1-bit bit map information stored in the bit map information storage may be compressed by means of a binary image coding method such as a run length, modified READ (MR, MMR), modified Huffman (MH), or JBIG coding method. Further, the information in the area where the absolute difference values are greater than the given parameter may be compressed by means of an adaptive Huffman coding process including a plurality of Huffman tables as the amount of predicted information.
According to still another aspect of the present invention, there is provided a system for compressing motion image information, including entropy coding means or circuit for reducing redundant information between frames by means of comparing spatially or temporally adjacent pixels to each other and outputting differential information, the system including: bit map information storage means or circuit for comparing pixels t and corresponding pixels txe2x88x921 to each other between frames pixel by pixel, detecting an area where the absolute values of pixel differences are greater than a given parameter, and storing the area and the other area into the form of a 1-bit bit map; and information compression means or circuit for compressing information in the area indicated, by the bit map stored in the bit map information storage circuit, as being greater in the absolute difference value between pixels t and txe2x88x921 than the parameter P.
According to still another aspect of the present invention, there is provided a system for compressing motion image information, including entropy coding means or circuit for reducing redundant information between frames by means of comparing spatially or temporally adjacent pixels to each other and outputting differential information, the system including: bit map information storage circuit for comparing pixels t and corresponding pixels txe2x88x921 to each other between frames pixel by pixel, detecting an area where the absolute values of pixel differences are greater than a given parameter, and storing the area and the other area into the form of a 1-bit bit map; and information compression means or circuit for compressing information in the area indicated, by the bit map stored in the bit map information storage circuit, as being greater in the absolute difference value between pixels t and txe2x88x921 than the parameter P, and for processing (deleting) pixels in the other area as those having no change between frames.
Preferably, the 1-bit bit map information stored in the bit map information storage circuit is compressed by means of a binary image coding method such as a run length, modified READ (MR, MMR), modified Huffman (MH), or JBIG coding method.
The information compression means or circuit for compressing information in the area where the absolute difference values are greater than said parameter P may perform information compression by means of an adaptive Huffman coding process including as many Huffman tables as the amount of predicted information.
The entropy coding means or circuit may include adaptive arithmetic coding circuit which has as many arithmetic tables as the amount of predicted information and which performs coding in accordance with an arithmetic table selected from the plurality of arithmetic tables.
According to still another aspect of the present invention, to achieve the above-described object, there is provided a method of compressing motion image information, by means of comparing spatially or temporally adjacent pixels to each other and outputting differential information thereby reducing redundant information between frames, the method including the steps of: comparing pixels treated on a block-by-block basis, each block including 2xc3x972 pixels, with corresponding pixels of another frame, detecting an area where the absolute values of differences are greater than a given parameter, and storing the detected area and the other area into the form of a 1-bit bit map; and compressing information in the area where the absolute values of differences are greater than the parameter.
According to still another aspect of the present invention, to achieve the above-described object, there is provided a method of compressing motion image information, by means of comparing spatially or temporally adjacent pixels to each other and outputting differential information thereby reducing redundant information between frames, the method including the steps of: comparing pixels treated on a block-by-block basis, each block including 2xc3x972 pixels, with corresponding pixels of another frame, detecting an area where the absolute values of differences are greater than a given parameter, and storing the detected area and the other area into the form of a 1-bit bit map; and compressing information in the area where the absolute values of differences are greater than the parameter and processing (deleting) the other area, where the absolute values of pixel differences are not greater than the parameter, as an area where there is no change in pixel value between frames.
When 2xc3x972 pixel data input to an encoder between frames are represented by A, B, C, and D, output data a, b, c, and d may be determined and a 2xc3x972 bitmap may be produced such as a=A+B+C+D, b=Axe2x88x92B+Cxe2x88x92D, c =A+Bxe2x88x92Cxe2x88x92D, and d=axe2x88x924D. Furthermore, decoded output data may be produced such as 3A≈a+b+c=3A+B+Cxe2x88x92D, 3B≈axe2x88x92b+c=A+3Bxe2x88x92C+D, 3C≈a+bxe2x88x92c=Axe2x88x92B+3C+D, and 3D≈axe2x88x92bxe2x88x92c=xe2x88x92A+B+C+3D.
Preferably, intraframe difference presence/absence information is given in the form of bitmap information corresponding to respective 2xc3x972 blocks in a frame, wherein it is determined whether there is a difference between frames by comparing the root-mean-square error of (three) data input to an encoder, that is ((A-Axe2x80x2)2+(B-Bxe2x80x2) 2+(C-Cxe2x80x2)2)xc2xd, with a parameter, and, if it is determined that there is a difference between frames, a corresponding bit of said intraframe difference presence/absence information is set.
Preferably, the 1-bit bitmap information stored in the bitmap is compressed by means of a binary image coding method such as a run length, modified READ (MR, MMR), modified Huffman (MH), or JBIG coding method.
Furthermore, information in the area where the absolute difference values are greater than the parameter may be compressed by means of an adaptive Huffman coding process including as many Huffman tables as the amount of predicted information.
According to still another aspect of the present invention, to achieve the above-described object, there is provided a system for compressing motion image information, including entropy coding circuit for reducing redundant information between frames by means of comparing spatially or temporally adjacent pixels to each other and outputting differential information, the system including: bitmap information storage circuit for comparing pixels t treated on a block-by-block basis, each block including 2xc3x972 pixels, with corresponding pixels txe2x88x921 of another frame, detecting an area where the absolute values of differences are greater than a given parameter, and storing the detected area and the other area into the form of a 1-bit bit map; and information compression circuit for compressing information in the area indicated, by the bitmap stored in the bitmap information storage circuit, as being greater in the absolute difference value between pixels t and txe2x88x921 than the parameter.
According to still another aspect of the present invention, to achieve the above-described object, there is provided a system for compressing motion image information, including entropy coding circuit for reducing redundant information between frames by means of comparing spatially or temporally adjacent pixels to each other and outputting differential information, the system including: bitmap information storage circuit for comparing pixels t treated on a block-by-block basis, each block including 2xc3x972 pixels, with corresponding pixels txe2x88x921 of another frame, detecting an area where the absolute values of differences are greater than a given parameter, and storing the detected area and the other area into the form of a 1-bit bit map; and information compression circuit for compressing information in the area indicated, by the bitmap stored in the bitmap information storage circuit, as being greater in the absolute difference value between pixels t and txe2x88x921 than the parameter, and for processing (deleting) pixels in the other area as those having no change between frames.
Preferably, in this system, the 1-bit bitmap information stored in the bitmap information storage circuit is intraframe difference presence/absence information corresponding to respective 2xc3x972 blocks in a frame, and said intraframe difference presence/absence information is compressed by means of a binary image coding method such as a run length, modified READ (MR, MMR), modified Huffman (MH), or JBIG coding method.
The information compression circuit for compressing information in the area where the absolute difference values are greater than the parameter may perform the information compression by means of an adaptive Huffman coding process including as many Huffman tables as the amount of predicted information.
The entropy coding circuit may include adaptive arithmetic coding means or circuit which has as many arithmetic tables as the amount of predicted information and which performs coding in accordance with an arithmetic table selected from the plurality of arithmetic tables.
The method and system for compressing motion image information according to the present invention are characterized in that pixels are treated on a block-by-block basis, each block including 2xc3x972 pixels, and that the pixels which are spatially or temporally adjacent are compared to each other, and differential information is output thereby reducing redundant information between frames. That is, pixels t in a frame are compared with corresponding pixels txe2x88x921 in a previous frame, pixel by pixel, to detect an area where the absolute difference values are greater than the parameter P. The detected area where the absolute difference values are greater than the parameter P and the other area are stored in the form of the 1-bit bit map.
In the entropy coding process, codes which will appear in successive frames are predicted, and small deviations from predicted codes are output thereby reducing the redundancy of information. The other information is compressed by means of adaptive Huffman coding or adaptive arithmetic coding in which coding is performed on the basis of a table selected from a plurality of tables in accordance with predicted information.